Application of α and n plots to N 2 adsorption isotherms of activated carbons

The application of the n and α methods to two different groups of N2 adsorption isotherms of activated carbons has been studied. The chemical nature of the adsorbent and the adsorbate and the adsorbent-adsorbate interactions have been established as two different means of assessing the standard N2 adsorption isotherms of non-porous carbon. The application of both criteria to N2 adsorption isotherms of activated carbons gave deviations at low and high relative pressures; these deviations were not significant in the evaluation of the micropore volumes and non-microporous surface areas of the carbons. Alternatively, the comparison between micropore volumes obtained by applying the Dubinin–Raduskevich (DR) equation and those from the n and α plots showed different results relating to the pore-size distributions of the carbons. Some α plots showed two straight portions, that located at lower α values being the most appropriate for evaluating the micropore volumes. In general, α and n plots have been shown to be more useful than the DR equation for analysing the N2 adsorption isotherms of highly activated carbons.